The present invention relates to a lock mechanism designed for mortise mounting in a door assembly including a door and frame. More particularly, the present invention relates to a lock mechanism which operates even in the presence of a force applied to the door.
A number of security locks are available for mortise mounting in door assemblies. An example of such a lock mechanism, referred to as a security lock, is shown in U.S. Pat. No. 4,237,711 to Kambic, assigned to the assignee of the present invention. The device as shown in Kambic utilizes a retractable latch Dolt and a biased deadlock latch associated with the latch bolt to urge the deadlock member into a locking position. A drive lever is associated with the latch bolt and the deadlock latch. A solenoid is used to move the drive lever and thereby move the associated latch bolt if it is not limited by the position of the deadlock latch. The lock mechanism is retained in the door frame with the latch bolt projecting into a recess formed in an opposing surface of the door frame.
Such security locks are valuable for locking doors in applications such as correction facilities, restricted access areas, and other security applications to control access. In these applications, a security lock may be connected to a remote switch such that the switch operates the solenoid associated with the drive lever. When the door is closed and the latch bolt is the locked position projecting into the recess of the opposed door frame, the deadlock latch is engaged to prevent movement of the latch bolt out the recess. The deadlock latch prevents tampering with the door by way of tools or other devices which might otherwise be positioned between the door and frame to displace the latch bolt from the recess.
When access is permitted the remote switch is activated thereby driving the solenoid to disengage the deadlock latch and move the driver lever to retract the latch bolt into the lock mechanism. Retracting the latch bolt into the lock mechanism removes the latch bolt from the corresponding recess after which the door can be moved relative to the frame.
While this type of operation may be satisfactory under many circumstances, the type of solenoid used to drive the lock mechanism may be limited in driving power. Basically, the solenoid functions quite well when the latch bolt fits into the recess without interference or when side loads are not applied to the door. The solenoid operates when the remote switch is activated to electrically displace a shaft in the solenoid thereby operating the latch bolt by way of the connecting linkage therebetween. When the remote switch is released, the solenoid returns the latch bolt to the extended position by way of a spring operated return in the solenoid assembly. The driving force of the solenoid is limited by the ability to displace the shaft in the solenoid and the strength of the return spring in the solenoid assembly.
Under some circumstances, it is important to be able to operate the lock mechanism in the presence of forces applied transversely to the door and latch bolt. For example, if the latch bolt does not properly fit as a result of dimensional differences between the door and frame, the solenoid may not provide sufficient driving power to operate the latch bolt. Similarly, if a force is applied transversely to the surface of the door, the forces tend to be concentrated at the latch bolt. The concentrated forces between the latch bolt and the recess prevent the latch bolt from being retracted by the solenoid if such forces are greater than the driving force of the solenoid. Forces may be applied to a door intentionally such as when an inmate wants to prevent the door from opening or unintentionally such as when the person passing through the door mistakenly pushes or pulls on the door opposite the direction of opening.
Further, the solenoid is limited in its operation in holding the latch bolt in an opened position. In the solenoid operated mechanism, the solenoid must be activated in order to hold the latch bolt in the open position. If the latch bolt is to be held in an open position for an extended period of time, the solenoid must be operated continuously for a corresponding extended period of time. It is undesirable to maintain a solenoid in the activated condition for extended periods since this can lead to excessive strain or wear on the solenoid. Alternatively, the solenoid must be operated each time the door is to be opened. It should be noted that in an application where the solenoid is not to be operated for extended periods of time, the solenoid operated lock functions in an acceptable manner without undue wear or strain on the solenoid. However, there are applications where it is desirable to maintain the latch bolt in the open, unlocked or retracted position.
As an additional matter, it would be desirable to provide a mechanical device to retain the latch bolt in a retracted position. It would also be desirable to provide a mechanical holdback device for the latch bolt which is automatically disengaged by appropriate circumstances such as the door closing against the jamb.